Cooperative interaction of CST and RECQ4 resolves G‐quadruplexes and maintains telomere stability

Abstract

Human CST (CTC1‐STN1‐TEN1) is a ssDNA‐binding complex that interacts with the replisome to aid in stalled fork rescue. We previously found that CST promotes telomere replication to maintain genomic integrity via G‐quadruplex (G4) resolution. However, the detailed mechanism by which CST resolves G4s in vivo and whether additional factors are involved remains unclear. Here, we identify RECQ4 as a novel CST‐interacting partner and show that RECQ4 can unwind G4 structures in vitro using a FRET assay. Moreover, G4s accumulate at the telomere after RECQ4 depletion, resulting in telomere dysfunction, including the formation of MTSs, SFEs, and TIFs, suggesting that RECQ4 is crucial for telomere integrity. Furthermore, CST is also required for RECQ4 telomere or chromatin localization in response to G4 stabilizers. RECQ4 is involved in preserving genomic stability by CST and RECQ4 disruption impairs restart of replication forks stalled by G4s. Overall, our findings highlight the essential roles of CST and RECQ4 in resolving G‐rich regions, where they collaborate to resolve G4‐induced replication deficiencies and maintain genomic homeostasis. image CST plays a crucial role in engaging RECQ4 with telomeres, enabling efficient resolution of G4 structures and restarting stalled replication forks. Their cooperative action addresses G4‐induced replication challenges, preserving genomic stability and homeostasis. RECQ4 and CST interact to unwind G4s, thereby resolving replication challenges and maintaining genomic stability. Depletion of RECQ4 leads to G4 accumulation at telomeres, resulting in telomere dysfunction. CST is essential for stabilizing RECQ4 at telomeres, irrespective of telomerase presence.